Paramagnetic molecules

The effects of an uncompensated electron are (1) to split the molecule s spectral lines into doublets, or in the case of certain diradicals, into triplets, (2) to make the molecule paramagnetic, (3) to catalyze the conversion of para and ortho hydrogen molecules, and (4) to cause paramagnetic resonance absorption. 

The pairing of electrons in the MOs can manifest itself in certain physical properties of the molecule. Paramagnetism results when there are unpaired electrons in the molecular orbitals. Paramagnetic molecules magnetize in magnetic fields due to the alignment of unpaired electrons. Diamagnetism occurs when there are all paired electrons in the MOs. We will revisit these properties in Chapter 6. 

Construct the molecular orbital diagram for diatomic nitrogen, N2. Is this molecule paramagnetic or diamagnetic ... 

Nitric oxide in its gaseous state exists as a monomeric species which possesses an unpaired electron, rendering the molecule paramagnetic. In terms of simple MO theory this electron is placed in a 7i-antibonding orbital (Figure 1) so that electron configuration is Jt)6(Jt ). Thus,... 

Oxygen is a colorless, tasteless, odorless gas of 02 molecules, which condenses to a pale blue liquid at — 183°C (Fig. 15.8). Although 02 has an even number of electrons, two of them are unpaired, making the molecule paramagnetic in other words, it behaves like a tiny magnet and is attracted to a magnetic field. 

The NO molecule has the electron configuration (crg)2(cru)2(crg, TTuf Ti The unpaired 77 antibonding electron renders the molecule paramagnetic and partly cancels the effect of the 77-bonding electrons. Thus the bond order is 2.5, consistent with an interatomic distance of 1.15 A, which is intermediate between the triplebond distance in NO+ (see later) of 1.06 A and representative double-bond distances of -1.20 A. 

Nitric Oxide (NO) Odd electron molecule, paramagnetic in gaseous state but diamagnetic in solid state due to dimeric structure, Bond order 2.5... 

Amongst other spectroscopic teclmiques which have successfiilly been employed in situ in electrochemical investigations are ESR, which is used to investigate electrochemical processes involving paramagnetic molecules, Raman spectroscopy and ellipsometry. 

Paramagnetism implies the presence of single, unpaired, electrons. Hence nitrogen oxide is paramagnetic and so is any other molecule or ion containing unpaired electrons. If the total number of electrons in an ion or molecule is odd. then it must be paramagnetic but some molecules (e.g. Oj and ions have an even number of electrons and yet are paramagnetic because some of them are unpaired. 

The structure of nitrogen dioxide contains an unpaired (odd) electron and the molecule is consequently paramagnetic. The odd electron is not localised on any atom and the structure can be best represented as a resonance hybrid of the structures ... 

The aqueous solution is safe to handle, the dissolution being essentially physical. On standing in sunlight the solution slowly decomposes to a mixture of acids. In alkaline solution a mixture of chlorate(lll), CIO2, and chlorate(V), CIO J, ions is rapidly produced. Chlorine dioxide is paramagnetic, the molecule containing an odd electron and having a structure very like that of NOj (p. 231). 

The O oxidation state is known in vanadium hexacarbonyl. V(CO)(,. a blue-green, sublimable solid. In the molecule VfCO), if each CO molecule is assumed to donate two electrons to the vanadium atom, the latter is still one electron short of the next noble gas configuration (krypton) the compound is therefore paramagnetic, and is easily reduced to form [VfCO, )]. giving it the... 

The addition of paramagnetic species, such as the metal ions Cu ", Mn, or CF", can have dramatic effects on both the observed spectmm and the relaxation behavior of a molecule. The added ion reduces nuclear relaxation times, and permitting more rapid data collection. In addition, faster relaxation rates minimize NOE effects in the spectra, which can be useful in obtaining quantitative intensity data. The most widely used reagent for this purpose is chromium acetylacetonate [13681 -82-8] known as Cr(acac)2. Practically speaking, the use of such reagents requires care, because at... 

Nitric Oxide. Nitric oxide [10102-43-9] NO, is a ubiquitous intracellular and intercellular messenger serving a variety of functions including vasodilation, cytotoxicity, neurotransmission, and neuromodulation (9). NO is a paramagnetic diatomic molecule that readily diffuses through aqueous and hpid compartments. Its locus of action is dictated by its chemical reactivity and the local environment. NO represents the first identified member of a series of gaseous second messengers that also includes CO. 

For example, in Ni(CO) nickel metal having 28 electrons coordinates four CO molecules to achieve a total of 36 electrons, the configuration of the inert gas krypton. Nearly every metal forming a carbonyl obeys the 18-electron rule. An exception is vanadium, forming a hexacarbonyl in which the number of electrons is 35. This carbonyl, which has a paramagnetism equivalent to one unpaired electron, however, readily adds one electron to form a closed valence shell complex containing the V(CO)(, anion. 

Many nitroxides are very stable under normal conditions, and heterolytic reactions can be carried out on other fimctional groups in the molecule without destroying the nitroxide group. Nitroxides are very useful in biochemical studies by virtue of being easily detected paramagnetic probes. ... 

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